Inverse Elastic Shell Design with Contact and Friction

SessionFabulously Computed Fashion

Event Type

Technical Papers

TimeWednesday, 5 December 20184:15pm - 4:41pm

LocationHall B5(1) (5F, B Block)

DescriptionWe propose an inverse strategy for modeling thin elastic shells

physically, just from the

observation of their

geometry. Our algorithm takes as input an arbitrary target mesh,

and interprets this configuration automatically as a stable

equilibrium of a shell simulator under gravity and frictional

contact constraints with a given external object. Unknowns are the

natural shape of the shell (i.e., its shape without external forces)

and the frictional contact forces at play, while the material

properties (mass density, stiffness, friction coefficient) can be

freely chosen by the user. Such an inverse problem formulates as an

ill-posed nonlinear system subject to conical constraints. To

select and compute a plausible solution, our inverse problemsolver

proceeds in two steps. In a first step, contacts are reduced to

frictionless bilateral constraints and a natural shape is retrieved

using the adjoint method. The second step uses this result as an

initial guess and adjusts each bilateral force so that it projects

onto the admissible Coulomb friction cone, while preserving global

equilibrium. To better guide minimization towards the target, these

two steps are applied iteratively on a degressive regularization of

the shell energy.

We validate our approach on simulated examples with reference material

parameters, and show that our method still converges well for

material parameters lying within a reasonable range around the

reference, and even in the case of arbitrary meshes that are not

issued from a simulation. We finally demonstrate practical inversion

results on complex shell geometries freely modeled by an artist or automatically captured from real objects, such as posed garments or soft accessories.

physically, just from the

observation of their

geometry. Our algorithm takes as input an arbitrary target mesh,

and interprets this configuration automatically as a stable

equilibrium of a shell simulator under gravity and frictional

contact constraints with a given external object. Unknowns are the

natural shape of the shell (i.e., its shape without external forces)

and the frictional contact forces at play, while the material

properties (mass density, stiffness, friction coefficient) can be

freely chosen by the user. Such an inverse problem formulates as an

ill-posed nonlinear system subject to conical constraints. To

select and compute a plausible solution, our inverse problemsolver

proceeds in two steps. In a first step, contacts are reduced to

frictionless bilateral constraints and a natural shape is retrieved

using the adjoint method. The second step uses this result as an

initial guess and adjusts each bilateral force so that it projects

onto the admissible Coulomb friction cone, while preserving global

equilibrium. To better guide minimization towards the target, these

two steps are applied iteratively on a degressive regularization of

the shell energy.

We validate our approach on simulated examples with reference material

parameters, and show that our method still converges well for

material parameters lying within a reasonable range around the

reference, and even in the case of arbitrary meshes that are not

issued from a simulation. We finally demonstrate practical inversion

results on complex shell geometries freely modeled by an artist or automatically captured from real objects, such as posed garments or soft accessories.